Though she’s only six, Eloise may be among the most famous residents of New York’s swanky Plaza Hotel. The New York Historical Society has created a whimsical exhibition, Eloise at the Museum, to celebrate her literary tenure. And the boutique show is a winner. The brainchild of Kay Thompson, a renowned vocal coach and cabaret star, Eloise was initially part of her nightclub act. But such was the little girl’s charm, she debuted in print in 1955, two years before Dr. Seuss’ C